1. Field of the Invention
The present invention relates to thermal imaging, and more specifically, it relates to a method for detecting an underground object surrounded by a host material.
2. Description of Related Art
Dual Band Infrared (DBIR) imaging has numerous advantages over conventional thermal imaging, which utilizes only a single band. Conventional thermal imaging is difficult to interpret for three reasons:
1. It yields imprecise information that is insensitive to the subtle heat flow anomalies produced by subsurface objects.
2. It fails to distinguish between surface emissivity clutter and temperature-related heat flows.
3. Spatially-varying surface reflections (emissivity-related noise), typically equivalent to a one or two degree Celsius temperature difference, cannot be removed by using a single passive thermal IR band even when used in conjunction with another active-laser reflectance IR band.
DBIR imaging was used to detect buried land mines by exploiting temperature differences between the mine site and the surrounding soil. U.S. Pat. No. 4,005,289 describes this method, and its content is incorporated herein by reference. See N. K. Del Grande et al., “Buried Object Remote Detection Technology For Law Enforcement, in Surveillance Technologies, SPIE 1479, p. 335, 1991,” which notes the difficulty of removing clutter from corrected temperature maps lacking thermal inertia diagnostics.
Thermal inertia diagnostics were used in conjunction with DBIR imaging to map flaws in heated structures (delamination gaps in bridge decks and corrosion gaps in aircraft) by exploiting thermal differences between the flaw and the structural material. U.S. Pat. No. 5,444,241, incorporated herein by reference, describes this method.